Thermochemical cutting and scarfing powder



Patented May 27, 1952 THERMOCHEMICAL CUTTING AND SCARFING POWDER Robert L. Wagner, Niagara Falls, N. Y., assignor, by mesne assignments, to Union Carbide and Carbon Corporation, a corporation of New York No Drawing.

Original application March 24, 1945, Serial No. 584,715.

Divided and this application August 5, 1948, Serial No. 42,654

2 Claims.

This invention relates to adjuvant powders suitable for thermochemically removing metal by a stream or jet of oxygen from heated bodies of metals and alloys which are immune to or resist progressive oxidation by the conventional thermochemical metal-removing action of only a preheating flame and a stream or jet of oxygen. Examples of such oxidation resistant metal bodies are ferrous metals such as stainless steel and cast iron, non-ferrous metals such as copper, aluminum, and nickel, and various alloys.

Previous attempts to thermochemically flame machine a surface layer of metalfrom a body of steel containing over 10% chromium to eliminate surface defects such as seams, snakes, and scabs, or to flame machine special contours in such an alloy steel body, have met with little or no success. However, stainless steel plates -have been thermochemically cut by placing a mild steel plate over the stainless steel plate, and flame cutting through the mild steel plate so that the molten slag from the mild steel kerf flows into the kerf in the stainless steel. This procedure is slow, large amounts of mild steel are wasted, and cuts of poor quality are produced. Another cutting procedure has involved moving an ordinary cutting torch in short strokes back and forth along the line of cut with a sawing motion in such a way to advance the torch intermittently a short forward increment followed by a relatively shorter reverse or backward movement. This method also is slow, inaccurate, uneconomical, and results in the formation of wide kerfs and rough cut surfaces. Even when the chromium content is between 5% and there is considerable resistance to flame cutting by conventional procedures.

A surface layer of metal likewisepould not be removed from cast iron by any prior known thermochemical method, and the cast iron could be thermochemically cut only with difiiculty. In cutting, the cutting torch was moved from side to side in a wide arc as it was advanced along the kerf, so that a wide rough kerf was produced, large amounts of metal were removed, and excessive amounts of cutting oxygen were used.

Non-ferrous metals have been difiicult or impossible to cut or machine thermochemically, although cutting solely by melting has sometimes been done. For instance, a bar of substantially pure nickel cannot be progressively oxidized and cut by the usual oxy-acetylene cutting method, nor can bars of copper or aluminum. Also, corrosion and oxidation resistant alloys such as 2 nickel-base alloys containing molybdenum, nickel-base alloys containing molybdenum and chromium, cobalt-chromium-tungsten alloys, and various silicon bronzes cannot be successfully cut or machined by conventional thermochemical technique.

Among the objects of this invention are to provide a novel adjuvant powder for thermochemically removing metal from metal and alloy bodies which are immune to or resist progressive oxidation by the sole action of a stream of oxygen upon a heated portion thereof as in ordinary flame cutting; to provide such a powder whereby metal removal can be carried out with greater speed, accuracy, economy, and neatness than formerly; to provide such a powder which can be used successfully under widely varying conditions on metal bodies of different compositions; to provide such a powder by which a metal removing reaction can be carried steadily and continuously across a resistant of immune metal body without special manipulation of a torch, in a manner similar to the thermochemical removal of metal from ordinary carbon steels; to provide a powder which is effective both for removing surface metal from resistant or immune metal bodies, as for deseaming, gouging, or otherwise flame machining them, and for cutting deep narrow kerfs in resistant or immune metal bodies, as for severing them.

In accordance with the invention, metal is thermochemically removed from a resistant or immune metal body by applying an oxygen jet against'a heated zone of action on the body while concurrently and continuously flowing a stream of finely-divided adjuvant material composed principally of iron into the zone of action so as to oxidize part of the constituents of the body and produce reaction products sufficiently fluid to be expelled by the oxygen jet, sometimes augmented by the force of gravity. The adjuvant material burns readily in oxygen to liberate intense heat, and forms compounds which flux refractory oxides.

Successive portions of the metal body on a path extending along its surface can be thermochemically removed by effecting a steady and continuous relative movement or travel between the body and the jet of oxygen across the surface. Heating of the zone of action preferably is accomplished by oxy-acetylene flames. In flame machining operations, wherein only metal near the surface is removed, a sufiiciently fluid reaction product is one which can be blown ahead 1 of the reaction zone by the oxygen jet to expose a fresh metal surface to the jet, and to preheat the surface portion to be removed next. In cutting operations, such as severing, sufiiciently fluid reaction products are those which can be blown through and out of the kerf, thus exposing fresh metal surfaces against which the oxygen jet impinges.

Flame machining to remove surface metal is carried out by advancing along the surface in the direction of gas flow a low velocity oxygen jet directed obliquely at a' small angle against successive heated zones on the surface of the metal body, while introducing the novel finelydivided material into the successive zones. Here also heating is preferably accomplished by applying one or more oxy-acetylene flames to the surface. In this procedure the. oxygen. .i'et. y locity generally is maintained less than 9980 ft./sec. (the acoustic velocity in oxygen) as it leaves the blowpipe nozzle.

In flame severing or either cutting operations a. high. velocity oxygen i'et preferably flowing at orelbove. the. acoustic velocity is directed at a large angle, such. as. against the. hot metal while. continuously introducing the finelydivided material into the reaction zone where the oxygen impinges. In severing, the oxygen jetpasses comp etely thro h'the body of me and f rms. a eep kerf. which. is advanced alon a. selected; path. by steadily 'adyancin the xyen let "so; as. to impinge against successive heated zones of the, body. If: a 'kfilgf extending only par ly throu h the body; is w nte h jet is advanced: at. a. =1 to. rapid enou h o. p ev n comp tc-ncnet ation.

her accordanc with this in en-tionz,

nor-e1 finely divided adjuvant. material is: carried into the reaction zone in close association with thenietal-removm oxy en itself. which pplated in lar e. volume suificient to. leave foroxidizing at ieast- @art of the resistant metal. an abundant. excess of oxy en over that. consumed for burnin diuyantniaterialv The minim m ratio. of: oxygen to combustible. adiilVan-t material for: succ sful. m tal removal, will vary somewhat for different materials and different. composioi: the metal bodies irom which metal is. to he rammed... ratio can. be determined empirically and. thereaiter p... ision should. be. made for maintaining. the ratio or oxygen. to. adi -ivant material. well above. the minimum so hat: a. lar e ce s. or oxy en is. available. for oxidizuig the. resistant metal body.

finely-d v ed 'adiuvant. material may e. brought into association. with the oxygen in any suitable manner- ='either in a blowpipe nozzle or just "outside of the nozzle after the oxygen emerges therefrom. Each procedure has special advantages for certain metal-removing ope-rations to he described hereinafter. Introducing the adiuvanjt material with the preheating combustible. gas mixture is undesirable because of the possibility of flashbacks into the blowpipje, which would cause, the adjuvant material, to burn or meltv within the 'blowpipe and clog the passsage For thermochemically cutting or desurfacing oxidation resistant steels. such as heat resistant steel containing about 25% chromium, cutlery steel containing, 12% to 14% chromium, and particularly austenitic. stainless steels, such. as those. containing approximately 18% chromium and 8 nickel or manganese, powdered iron and mild steel have been used successfully. These 4 adjuvant materials may also be used for thermochemically cutting or machining cast iron.

For thermochemically removing metal from non-ferrous metal bodies, powdered iron has given particularly good results in cutting nickel, copper, aluminum, a cobalt-chromium-tungsten alloy, an alloy containing over 95% copper with the remainder principally silicon, and brass containing about 50% copper and 50% zinc. For most effective results it is necessary to preheat copper, aluminum, and nickel bodies prior to cutting. Some progress can be made. however, on cold nickel and aluminum bodies.

Iron powders are again useful for cutting substantially' non-ferrous alloys having only slight amounts of iron. such as a nickel-base alloy containing approximately 20% molybdenum, 20%. iron, and 60% nickel; one containing approximately- 30% molybdenum, 5% iron, and 65% nickel; and one containing approximately 17% molybdenum, 8% iron, 60% nickel, and 15% chromium.

Although the novel method of the invention can be performed successfully with many dif ferent finely-divided adjuvant materials, outstanding; results with respect to high speediow cost, and good characteristics of the. resultant metal surface have been provided. on most metals by'powdered iron.

It has been iouncl that; in thermochem-ically removing metal from resistant metal bodies the cost, the speed of progress, and the character of the metal surface are afiected to a surprisingly large extent by the physical fineness of the adjuvant powder. When impure iron powder 111* mixed with other ingredients is suiiiciently -fi-ne the thermochemical removal of metal can pro ceed at. a rate considerably faster than. with coarse particles of the same. composition, almost as rapidly as with, an iron-ferromanganese mixture, and at considerably lower cost. Excellent results have been obtained with iron in the. form of I unbonded impure steel adjuvan-t powder-com"- prising by weight to metallic iron, 'less than. 0.20% carbon. balance incidental impurities. such as FeO, S102 and minor quantities oi other impurities. Such an adjuvant powder -desirably is prepared by reduction from. a. virgin oxidesuch. as iron ore, or {from an artificial iron oxide, such as mill scale, as by hydrogen, carbon monoxide, or natural gas. 0ne specific exampleof such an adjuvant powder had, the following; composition:

92.14% Fe (metallic) 3,60% FeO.

3.12% SiOz Balance-other impurities A careful-screeningof the impure iron powder to. eliminate coarse, particles is essential, and i: is particularly important. that all. of the screened powder pass. through a mesh screen (.0058- inch openings). and at least 70 %v by weight pass through a ZOO-mesh screen (1.0.029 inch openings). It; is also advantageous but not essentiai that at least 510% of the. powder by weight pass through. a. 300.. mesh screen (.0018 inch. openings) Using impure ironv adjuvant. powder of the above-described. chemical and physical analysis, the following results. were obtained. in cutting. stainless steel billets. "of the 18%; Cr-8;%1 Ni type when. separately discharging the-oxygen, adio 5 vant powder, and preheating gases from a blowpipe nozzle:

Thickness, Cutting Oz, Powder, Cutting Speed,

inches 7 cu. ft./hr. lbs/hr, in. 111111.

3 400 8. 8 4. 2 4 700 15. 4 5. 5 5 l, Q00 22. O 6. 4

Also using the same specificadjuvant powder an 18-8 stainless steel billet wasdeseamed by flame planing using 0.49 pound of powder, 13.7, cubic feet of oxygen, and 0.46 cubic foot of acetylene per pound of metal removed, by directing preheating flames, a low velocity oxygen jet, and a stream of powder obliquely against and along the surface of the billet in such a way as to remove metal and leave a shallow groove or furrow.

With the above-described impure iron adjuvant powder on 18-8 stainless steel, evidence indicates that if the oxygen-to-powder ratio decreases below 15 cu. ft. of oxygen to 1 pound of powder, so much of the oxygen is consumed in burning the powder that there is insufiicient oxygen left over for oxidation of the metal body, and metal removal is prevented or proceeds at an unsatisfactorily slow speed. In cutting, less than a 15 to 1 ratio also results in incomplete penetration. On the other hand, if the ratio of oxygen to powder increases beyond about 100 to l, insuflicient heat is produced and the slag is not liquid enough to be blown away by the oxygen jet.

The important influence of adjuvant powder particle size is strikingly illustrated by comparing with one another the oxy-powder factors determined by flame planing at similar speeds grooves of similar dimensions with powders of the same chemical composition but different degrees of fineness. Upon completing each of the several similar grooves the total oxygen and powder consumptions were determined and the resulting flgures expressed as the cubic feet of oxygen consumed per pound of powder at standard conditions of temperature and pressure, called the oxy-powder factor. Since an important influence on the economy of operation is the cost of adJuvant powder, the need for a relatively small powder consumption reflected in a high oxypowder factor is evident, and the higher the factor the lower is the cost of operation.

In a series of tests on austenitic Cr-Ni stainless steel involving flame planing grooves of various depths, the following results were obtained using an impure iron adjuvant powder having the screen analysis shown:

Screen Analysis Oxy-powder factor,

throughcu. ft. O1/lb. powder- (shallow (deep 100 mesh 200 mesh groove) groove) Per cent Per cent #1 100 30 17 37 #2 100 37 90 similar deep grooves. This indicates that the same performance requires more than twice as much coarse powder as fine powder, and the use of the fine powder consequently greatly reduces the cost of operation.

In tests on flame planing at similar speeds 0.075 inch deep similar grooves on 8" x 7" billets of 12% Ni-l7.5% Cr stainless steel using an adjuvant powder analyzing 88.45% metallic Fe, 6.64% FeO, 2.95% S102, 0.57% Mn, 0.089% S, 0.98% C, balance incidental impurities, the following results were obtained.

The critical effect of powder fineness on performance is emphasized by Examples #3 and #4 above showing that an increase of only 14% in the quantity of powder passing through a 200 mesh screen resulted in almost a 50% increase in the oxypowder factor and almost a 40% decrease in the quantity of powder required for equivalent performance.

In the foregoing tests speed was maintained constant to provide a comparison of powder consumptions. However, a finer powder also permits greater flame planing speeds than are obtainable with a coarser powder and the same or even a smaller oxy-powder ratio. For example, on cold stainless steel the maximum speed with a relatively coarse steel powder was 8 ft./min., but with the preferred fine powder described above a speed of 12 ft./min. was maintained with a smaller powder consumption.

Although the foregoing discussion of the effect of adjuvant powder particle size relates specifically to flame planing, this is only by way of example because the same principles apply to flame cutting and other procedures for thermochemically removing metal.

This application is a division of my application Serial No. 584,715, flled March 24, 1945, and entitled Thermochemically Removing Metal, now Patent No. 2,451,422, which issued October 12, 1948.

This application is also a continuation-inpart of my abandoned application Serial No. 456,667, filed August 29, 1942; and entitled Method of and Apparatus for Thermochemically Removing Metal.

I claim:

1. An unbonded flowable thermochemical cutting and scarfing adjuvant powder containing between and metallic iron, carbon less than 0.20%, and the balance oxides of iron and silicon and other impurities, said other impurities being present in amount less than 1%, said powder being sufiiciently fine that substantially all of it passes through a mesh screen and 70 to 74% of it passes through a 200 mesh screen.

2. An unbonded flowable thermochemical cutting and scarfing adjuvant powder containing between 80% and 95% metallic iron, carbon less than 0.20%, and the balance oxides of iron and silicon and other impurities, said other impurities being present in amount less than 1%, said powder being sufficiently fine that substantially all of it passes through a 100 mesh screen and 

1. AN UNBONDED FLOWABLE THERMOCHEMICAL CUTTING AND SCARFING ADJUVANT POWDER CONTAINING BETWEEN 80% AND 95% METALLIC IRON, CARBON LESS THAN 0.20%, AND THE BALANCE OXIDES OF IRON AND SILICON AND OTHER IMPURITIES, SAID OTHER IMPURITIES BEING PRESENT IN AMOUNT LESS THAN 1%, SAID POWDER BEING SUFFICIENTLY FINE THAT SUBSTANTIALLY ALL OF ITS PASSES THROUGH A 100 MESH SCREEN AND 70 TO 74% OF ITS PASSES THROUGH A 200 MESH SCREEN. 